Species of Anulocaulis have been considered to belong in a broadly circumscribed Boerhavia, the western A. annulatus most recently so in regional treatments. F. R. Fosberg (1978) argued for an inclusive Boerhavia, and suggested that workers emphasizing differences might wish to recognize segregate genera, as is done in this work.

Flowers of Anulocaulis, particularly in those species with large ones, are slightly bilaterally symmetric because of curvature of the tube, variation in the amount of curvature of the limb, and the downward sweep of the stamens and the style.